Zoom lens system and image taking apparatus including the same

Abstract

Provided is a zoom lens system includes, in order from an object side to an image side: a first lens unit having a positive refractive power; a second lens unit having a negative refractive power; a third lens unit having a positive refractive power; and a fourth lens unit having a positive refractive power, the second and fourth lens units move on an optical axis during zooming. The third lens unit includes, in order from the object side to the image side: a third A lens unit having a negative refractive power; and a third B lens unit having a positive refractive power, the third B lens unit including a positive lens and a negative lens being joined together. When curvature radii of surfaces of the cemented lens on the object side and the image side are R 3 A and R 3 B, respectively, the following condition is satisfied: 5<|(R 3 A+R 3 B)/(R 3 A−R 3 B)|<30.

1. A zoom lens system, comprising, in order from an object side to an image side:
 a first lens unit having a positive refractive power; 
 a second lens unit having a negative refractive power; 
 a third lens unit having a positive refractive power; and 
 a fourth lens unit having a positive refractive power, the second lens unit and the fourth lens unit moving along an optical axis during zooming, wherein: 
 the third lens unit comprises, in order from the object side to the image side:
 an aperture stop; 
 a first lens subunit having a negative refractive power; and 
 a second lens subunit having a positive refractive power which moves in a direction having a component in a direction perpendicular to the optical axis for moving an imaging position; 
 
 the second lens subunit comprises a cemented lens in which a positive lens and a negative lens are joined together; and 
 when curvature radii of surfaces of the cemented lens on the object side and the image side are R 3 A and R 3 B, respectively, a maximum aperture diameter of the aperture stop is Spa, a total thickness on the optical axis of the positive lenses configuring the second lens subunit is Dp, a total of lens thicknesses at a height from the optical axis of a half of the maximum aperture diameter of the negative lens that configures the second lens subunit at the wide angle end is Kn, a focal length of the third lens unit is f 3 , and focal lengths of an entire system at a wide angle end and a telephoto end are fw and ft, respectively, the following conditions are satisfied
   5<|( R 3 A+R 3 B )/( R 3 A−R 3 B )|<30, 
   0.44<( Dp+Kn )/ Spa< 0.60, and 
   3.6 <f 3/√{square root over (( fw·ft ))}<6.2.
 
 
 
     
     
       2. A zoom lens system according to  claim 1 , wherein when focal lengths of the first lens subunit and the second lens subunit are f 3 A and f 3 B, respectively, the following condition is satisfied
   1.3 <|f 3 A/f 3 B|< 2.5. 
 
     
     
       3. A zoom lens system according to  claim 1 , wherein:
 the first lens unit comprises a negative lens, a positive lens, a positive lens, and a positive lens in order from the object side to the image side; and 
 when a focal length of the first lens unit is f 1 , a focal length of an entire system at the telephoto end is ft, an Abbe number of a material of one positive lens in the first lens unit is ν1A, and an Abbe number of a material of another positive lens in the first lens unit is ν1B, the following conditions are satisfied
   0.7 <f 1 /ft< 1.0 
   65<ν1 A< 75
 
   70<ν1 B.  
 
 
 
     
     
       4. A zoom lens system according to  claim 1 , wherein the fourth lens unit comprises a positive lens on the object side, and a cemented lens in which a negative lens and a positive lens are joined together on the image side. 
     
     
       5. An image taking apparatus, comprising:
 a zoom lens system; and 
 a solid state image pickup element that receives light of an image formed by the zoom lens system, 
 the zoom lens system comprising, in order from an object side to an image side, 
 a first lens unit having a positive refractive power; 
 a second lens unit having a negative refractive power; 
 a third lens unit having a positive refractive power; and 
 a fourth lens unit having a positive refractive power, 
 the second lens unit and the fourth lens unit moving along an optical axis during zooming, wherein: 
 the third lens unit comprises, in order from the object side to the image side:
 an aperture stop; 
 a first lens subunit having a negative refractive power; and 
 a second lens subunit having a positive refractive power which moves in a direction having a component in a direction perpendicular to the optical axis for moving an imaging position; 
 
 the second lens subunit comprises a cemented lens in which a positive lens and a negative lens are joined together; and 
 when curvature radii of surfaces of the cemented lens on the object side and the image side are R 3 A and R 3 B, respectively, a maximum aperture diameter of the aperture stop is Spa, a total thickness on the optical axis of the positive lenses configuring the second lens subunit is Dp, a total of lens thicknesses at a height from the optical axis of a half of the maximum aperture diameter of the negative lens that configures the second lens subunit at the wide angle end is Kn, a focal length of the third lens unit is f 3 , and focal lengths of an entire system at a wide angle end and a telephoto end are fw and ft, respectively, the following conditions are satisfied
   5<|( R 3 A+R 3 B )/( R 3 A−R 3 B )|<30, 
   0.44<( Dp+Kn )/ Spa< 0.60, and 
   3.6< f 3/√{square root over ( fw·ft ))}<6.2.